1. Field of Invention
This invention is directed to systems and methods for authenticating documents.
2. Description of Related Art
There are a number of situations where a sender transmits a document to a receiver and wants to assure the receiver that the document has not been altered during the transmission. In other words, the sender wants to authenticate the document.
Paper documents are traditionally authenticated either through elaborate printing techniques, such as, for example, money, or through trusted signatures and stamps, such as, for example, notarizing by a public notary. The signing and verifying processes of these current methods are not automated and require human intervention. Nor are these processes very reliable.
There are more recent methods that work on digital document data. During verification, these methods are applied to paper documents by acquiring a scanned image of the printed authenticated document. The resulting scanned image is then verified using some known verification scheme. These techniques, unfortunately, do not work well because, when the document is scanned by the receiver, the resulting scanned image usually differs from the original document content used during authentication. This occurs due to the noise inherent in scanning a document. The noise introduced by scanning makes it difficult to construct an authentication scheme that is resilient in view of the noise.
A method that authenticates photo-identification cards and has to cope with noise being introduced due to scanning is disclosed in “Secure Identification Documents Via Pattern Recognition and Public-Key Cryptography”, by L. O'Gorman et al., IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 20, No. 10, pages 1097-1102, October 1998. However, the authentication signature disclosed by O'Gorman et al. has a file size that is linear to the size of the photograph. This method does not scale well as the size of a document increases. The method disclosed in O'Gorman et al. would create an authentication file that would be large in comparison to the document. This tends to render the O'Gorman et al. method inefficient.